Background
The author writes that "there is increasing concern in southern Africa about the possible decline of rainfall as a result of global warming," with some studies claiming that "average rainfall in Zimbabwe had declined by 10% or 100 mm during the last 100 years" and stating that this phenomenon was "due to global warming."

What was done
As a result of this concern and the claims associated with it, Mazvimavi "investigated the validity of the assumption that rainfall is declining in Zimbabwe," analyzing time series of annual rainfall and rainfall for the early part of the rainy season (October-November-December) and the mid to end of the rainy season (January-February-March) for the presence of trends using the Mann-Kendall test, while looking for change or break-points in the rainfall time series by means of the Pettitt test, all of which operations utilized rainfall data obtained from 40 observation stations with records beginning as early as 1892 and ending in the year 2000.

What was learned
The South African researcher reports that rainfall records for the 1892 to 2000 period at the 40 stations in Zimbabwe do not demonstrate evidence of changes in median, high or low rainfall during the early part of the rainy season, the mid-to-end part of the rainy season, or the whole year, noting that "other studies in Africa and Zimbabwe (New et al., 2006; Conway et al., 2008; Aguilar et al., 2009) made the same conclusion."

What it means
Mazvimavi thus concludes that climate change effects that have been predicted to be "due to global warming" are "not yet statistically significant within time series of total seasonal and annual rainfall in Zimbabwe," noting that "there is no proof that the average rainfall at each of these stations has changed."

References
Aguilar, E., Aziz Barry, E., Brunet, M., Ekang, L., Fernandes, A., Massoukina, M., Mbah, J., Mhanda, A., do Nascimento, D.J., Peterson, T.C., Thamba Umba, O., Tomou, M. and Zhang, X. 2009. Changes in temperature and precipitation extremes in western, central Africa, Guinea Conakry, and Zimbabwe. Journal of Geophysical Research 114: 1955-2006.

Conway, D., Persechino, A., Ardoin-Bardin, S., Hamandawana, H., Deulin, C. and Mahe, G. 2008. Rainfall and Water Resources Variability in Sub-Saharan Africa During the 20th Century. Working Paper 119, Tyndall Centre for Climate Change Research, University of East Anglia, United Kingdom.

New, M., Hewitson, B., Stephenson, D.B., Tsiga, A., Kruger, A., Manhique, A., Gomez, B., Coelho, C.A.S., Masisi, D.N., Kululanga, E., Mbambalala, E., Adesina, F., Saleh, H., Kanyanga, J., Adosi, J., Bulane, L., Fortunata, L., Mdoka, M.L. and Lajoie, R. 2006. Evidence of trends in daily climate extremes over Southern and West Africa. Journal of Geophysical Research 111: 1-11.